1. Field of the Invention
The present invention relates to a navigation server which supports a guidance of a mobile subject guided by a navigation apparatus on the basis of communication with the navigation apparatus, a navigation apparatus which guides the mobile subject on the basis of communication with the navigation server, and a navigation system comprised of the navigation server and the navigation apparatus.
2. Description of the Related Art
There has been disclosed an art (for example, refer to Japanese Patent Laid-open No. 2002-296042, paragraphs 0008 to 0009) in which differential information between map information of an old version and map information of a new version is transmitted from a navigation server to a navigation apparatus in accordance with the opening of a new road or the like, and the map information of the old version which is stored in a memory element of the navigation apparatus is updated to the map information of the new version according to the differential information.
From the viewpoint of curtailing communication cost or the like on the differential information transmitted from the navigation server to the navigation apparatus, there has been disclosed an art which transmits to the navigation apparatus only the differential information having high necessity to a user (for example, refer to Japanese Patent Laid-open No. 2006-065246, paragraphs 0009 to 0010 and FIG. 2). Specifically, the difference between the map information used respectively by the navigation apparatus and the navigation server is determined according to the difference between a length of a route (predicted travel distance) searched by the navigation apparatus and a length of a route searched by the navigation server according to an identical algorithm, respectively. Thereafter, according to the determination result on the difference between the map information, the differential information of an area along the route searched by the navigation server is transmitted to the navigation apparatus.
However, even though the map information used by the navigation apparatus and the navigation server are different, it is possible that the routes searched respectively by the navigation apparatus and the navigation server according to an identical algorithm are the same. Thereby, when a vehicle is positioned on a road which is not included in the map information used by the navigation apparatus, the search of a route by the navigation apparatus may end unsuccessfully. As a result, this may cause the update of the map information in the navigation apparatus according to the determination result on the difference between the routes searched respectively by the navigation apparatus and the navigation server to end unsuccessfully.